This application claims the priority of German Patent Document 199 10 892.7, filed Mar. 11, 1999, the disclosure of which is expressly incorporated by reference herein.
The present invention concerns a thermal spray coating method for creating a coating layer on the surface of a substrate, wherein at least one characteristic of the thermal spray coating method affecting the quality of the coating layer is recorded, controlled, and/or monitored by a digital camera. The present invention also concerns a device for quality assurance when creating a coating layer on the surface of a substrate by thermal spray coating which comprises a digital camera for recording, controlling, and/or monitoring at least one characteristic of the thermal spray coating method affecting the quality of the coating layer.
In the thermal spray coating method, typically an additive is melted onto or applied in molten form with the aid of a gas or gas mixture to the surface of the substrate to be coated.
A method and a device of this kind are described in our German patent application 198 20 195.8. The starting point in that application was to guarantee reproducibility; achievement of quality demands; and adherence to prescribed quality requirements by recording, controlling, and/or monitoring the parameters in thermal spray coating. To do so, relevant process parameters are measured, controlled and perhaps also documented. Such parameters could be, for example, gas flows (carrier gas and/or perhaps fuel gas); current strengths; the spraying distance; the spraying angle (angle between the coating jet and the substrate surface); the velocity of the coating jet relative to the substrate surface; the quantity of additive taken up; the quantity of sprayed powder or the wire feed rate; and the like.
Within the scope of this present invention, all known variants of thermal spray coating would in principle be feasible as process variants, for example, autogenous flame coating, high velocity flame coating, plasma coating, electric arc coating, detonation coating or laser coating, and also the thermal coating variant known as cold gas coating, which is a type of further development of high velocity coating (for example, as described in the European patent specification EP 0 494 533 B1). In cold gas coating, an additive is in powder form in which the powder particles are not melted in the gas jet during cold gas coating. Instead, the temperature of the gas jet is kept below the melting point of the additive powder particles.
In the device as described in our German patent application 198 20 195.9, a digital camera is provided for recording, controlling, and/or monitoring at least one characteristic of the thermal spray coating method affecting the quality of the coating layer. The digital cameras could be either digital image cameras or digital video cameras. The required recording, controlling, and/or monitoring could therefore be achieved by single images and/or video images combined together as sequences to make a film. The boundary between single images on the one hand and film on the other hand is not sharply defined. The lower Iimit for the frame frequency can be regarded as approximately 16 images per second given the slow response of the human eye.
The diagnostic for recording, controlling, and/or monitoring of characteristics of the thermal spray coating method affecting the quality of the coating layer, as described in our German patent application 198 20 195.9, allows quality assurance of the thermal coating process with relatively little effort yet with exceptional efficiency. So, for example, in companies where thermal coating is used and at the same time frequent changing of coating applications arises, the reproducibility of the coating layer can be guaranteed, and consistent quality of the coating layers very quickly achieved by a diagnostic that evaluates quality-influencing characteristics or parameters and/or quantitatively measures the spray coating method using image standards. It is important, due to the purely optical approach used, that the recording, controlling, and/or monitoring of the quality characteristics in no way whatsoever adversely affects the thermal spray coating method or damages the coating layer in any way. On the other hand, for example, it can be guaranteed even after a longer period of time that the same application is coated with the same coating accuracy if, for example, the characteristics of the image in the melting zone are identical to the previous ones.
The recording, controlling, and/or monitoring by a digital camera can be used to control and, if necessary, optimize one or more parameters. With digital technology, it is completely unproblematic to display and/or evaluate, during the running spray coating process, the recordings made for the purpose of recording, controlling, and/or monitoring the quality of the coating layer so that optimized control of the spray coating parameters can take place. This optimization of the parameters contributes to the economic efficiency of the thermal spray coating method because an ineffective high consumption of one or more of the materials required by the thermal spray coating method (e.g., gas volumes, additives) is avoided, thus allowing savings to be achieved.
In doing so, advantage can be taken of the many display possibilities that digital technology provides. Depending on the individual case, the various display variants—in particular computer processing or encoding—can provide particular advantages. The images or video recordings can in principle be presented in black and white or color. Mixed forms with, for example, partial color representation are also possible.
The task of the present invention is to provide a method and a device as described at the outset wherein the computer processing and/or encoding has been further developed and improved. In particular, the volume of information upon which the diagnostic is based is to be kept as small as possible or reduced so as to simplify handling, speed, and/or data storage.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing.